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Message:

> Estimated at 2.1 billion years ago:
> 
> https://cosmosmagazine.com/biology/study-dates-origin-of-photosynthesis-to-2-1-billion-years-ago
> 
> Peer into a plant cell and you’ll find the engine at its heart is a stowaway. In size, shape, and the genes it carries it resembles a bacterium: a cyanobacterium, to be precise.
>  
> It’s a very valuable stowaway. Known as a chloroplast, this cyanobacteria-like interloper carries the machinery for photosynthesis, the process by which plants use sunlight to power the synthesis of sugar. As a side effect, photosynthesis also produces the oxygen that we breathe and require for cellular respiration.
> 
> The evolution of this stowaway is believed to have occurred by a process called endosymbiosis, whereby a cyanobacterium was engulfed by a larger single-celled eukaryote – a more complex kind of cell that contains discrete organelles surrounded by membranes. Eventually a symbiotic relationship formed between the two which led to the development of photosynthetic plant cells. 
> 
> ***
> 
> The study revealed that the chloroplast diverged from its closest relative, the cyanobacterium Gloeomargarita, around 2.1 billion years ago. It also showed that the divergence occurred in a freshwater environment, rather than in a marine environment as previously thought, and that it took another 200 million years for the first photosynthetic eukaryote to evolve.
> 
> Dr Geoff McFadden, a researcher at the University of Melbourne who was not involved in the study, says it’s a significant step forward in our understanding.
> 
> “This study has a lot of credence due the number of genetic sequences used,”says McFadden. “It has provided a lot of evidence for a time point which was not previously known.”
> 
> McFadden did question the large gap in time between the endosymbiosis event and the evolution of the photosynthetic eukaryotes, suggesting that it is an area that should be further explored.
> 
> Comment: the same theory applies to the mitochondria as being engulfed energy-active bacteria. Without photosynthesis we would not have 21% oxygen in our atmosphere.